The Celestial Intervention Agency, a shadowy, unspoken of part of the Time Lord hierarchy. Beloved and loathed in equal measure by various Presidents and High Councils the millennias over. But they serve a very important function: they keep the time lines safe and clear - they do the darker, dirtier jobs that most Time Lords would prefer not to know even need doing.

CIA Sub-Coordinator Narvin has always taken his oath to uphold the Worshipful Laws of Gallifrey very seriously. But when he is sent on a mission to investigate the planet Bellascon, even he hasn't reckoned with the force of nature that is the Fourth Doctor, who has - one might say - his own way of dealing with things, and his own views on people like Narvin. But somehow the two must overcome their instincts and work together to stop the web of time being erased forever...

Directed by Gary Russell, producer Ian Atkins tells us more about bringing Seán Carlsen in to the Short Trips range.

“Narvin's very vocal fan following and Seán Carlsen being incredibly enthusiastic about all things Big Finish, were the start of Erasure. I'd been looking for a few Short Trips ideas that would flirt with other Big Finish Doctor Who ranges and characters, and at the time Seán Carlsen had come into the office to record a podcast with Nick Briggs. He got very excited about doing a Short Trip, and suggested I spoke to the current Gallifrey production team about what they could do with the character.

“Scott Handcock recommended that I approach Gary Russell, and before I knew it Gary and I were swapping notes about the Fourth Doctor and Adric’s return to normal space, and how perhaps their paths would cross with a young Narvin. Indeed, having Narvin as he's starting out has been a fascinating angle on this character, which Seán has really embraced, and which the Short Trips are all about.

“Appropriately for a season 18-set story, it's been full circle for me, as Gary's enthusiasm and support for my fanzine Land of Fiction back in 1985 helped sow the seeds for a lifetime's fascination with Doctor Who stories, something that's ultimately enabled me to embrace the Short Trips range with both hands."

Make sure you don’t miss this and all the other new Short Trips available on download (only) at £2.99 from Big Finish. Or you can save money with a subscription to the Short Trips range and get 12 stories for £30 a year.